Bluetooth® is a technology for low-power, low-bandwidth wireless connections between devices. Connected devices form a small network known as a piconet, with a master device and one or more slave devices. In Active Mode, a Bluetooth® device (BT device) participates actively on the transmission channel. The Bluetooth® core specifications v1.1, published Feb. 22, 2001 by the Bluetooth® special interest group (SIG) and the Bluetooth® core specifications v1.2, published Nov. 5, 2003, include provisions for three low-power modes to conserve battery life. These modes, in decreasing order of power requirements, are Sniff Mode, Hold Mode, and Park Mode.
While in the Sniff Mode, the device listens to the piconet at a reduced rate, related to three parameters: Sniff Interval, Sniff Attempt and Sniff Timeout. These parameters are programmable, providing flexibility for different applications. The Hold Mode is similar to the Park Mode, except that the device retains its Active Member Address, which distinguishes the device from other devices in the piconet. In the Park Mode, the device does not participate at all in the piconet, although the device's clock continues to run and remains synchronized to the master device.
If a user of a first device wants the first device to communicate wirelessly with a second device that is in Sniff Mode, the communications therebetween will be delayed until the second device has listened to the piconet during a Sniff Interval and has transitioned from Sniff Mode to Active Mode. For example, it may take the second device around 2 seconds to transition from Sniff Mode to Active Mode. In a situation where communication with the second device tends to happen in short bursts of about 2 to 5 seconds duration, the delay incurred by transitioning from Sniff Mode to Active Mode may cause the second device to appear sluggish to user-initiated activity.
Similar concerns may arise with devices compatible with other wireless communication protocols, a non-exhaustive list of examples for which includes ZigBee™ radio frequency identification (RFID), ultra wideband (UWB), IEEE 802.11 and various proprietary communication protocols.